It is well known to attach ducts to one another by situating corner plates in flanges formed at the end of each duct. The corner plates are situated and retained in the flanges such that an exposed portion of the corner plate with a hole defined therein can be aligned to a corner plate situated in the flange of another duct. A fastener, such as bolt, can be passed through the aligned holes in the corner plates and secured, attaching the corner plates and the respective ducts to one another. This method of attachment is shown and discussed in U.S. Pat. No. 4,466,641 to Heilman et al. and U.S. Pat. No. 4,542,923 to La Crosse et al.
Techniques have also been developed to automate the process of installing the corner plates on the ducts. Machines are now used to install the corner plates and fix them in place. These machines use automatic feeders in which corner plates are fed one by one from the bottom of a stack of corner plates. To facilitate the automatic feeding, the corner plates were reconfigured to facilitate the formation of an orderly stack; the automatic feeding process requires that the corner plates maintain repeatable and even vertical spacing when stacked. This requires the corner plates to be configured such that they do not nest within one another when stacked. To achieve the desired stacking and anti-nesting characteristics, vertical tabs were added to the corner plates. One example of a corner plate installation machine, automatic feeder, and related corner plate can be seen in U.S. Pat. Nos. 5,283,944 and 5,342,100 to Goodhue.
One drawback of the conventional corner plates equipped with tabs to achieve vertical separation is that they fail to provide lateral stability to the stack. Traditional tabs do nothing to prevent a corner plate from moving laterally relative to an adjacent corner plate in the stack, which could cause feeding problems. Additionally, the shape of the tabs impacts the anti-nesting characteristics and the reliability of the corner plates when used in an automatic feeder. It would be beneficial to have a corner plate that provides improved stacking and anti-nesting characteristics while also resisting lateral movement in a direction perpendicular to the feed direction.